In recent years, high brilliance LED having stronger light intensity and heat dissipation have been commercialized, and they have been widely used in general lighting applications. This is accompanied however by a problem of discoloration of the encapsulant caused by a corrosive gas. In order to solve this problem, Japanese Patent Application Publication No. 2005-272697 (IP Publication 1), for example, reports that an encapsulant excellent in heat resistance, light resistance and weather resistance is obtained through addition of hindered amine light stabilizer to a phenyl silicone resin. Also, Japanese Patent Application Publication No. 2009-215434 (IP Publication 2) proposes a silicone resin composition capable of preventing organic resin package from degrading and extending the life of LED, and this silicone resin composition contains a silicone resin (e.g., methyl silicone resin) which has two or more aliphatic unsaturated bonds in one molecule and does not have any aromatic hydrocarbon group but has an aliphatic hydrocarbon group as a substituent group.
However, these above-mentioned silicone resin compositions, while excellent in light resistance, heat discoloration resistance and shock resistance, exhibit large coefficients of linear thermal expansion and high gas permeability, so that it is known that a corrosive gas would attack and blacken the silver surface plated on the substrate used in an optical semiconductor device such as LED, and, as a result, would weaken the brightness of the LED; hence a further improvement is desired.
Also, Japanese Patent Application Publication No. 2000-17176 (IP Publication 3) reports on an optical purpose silicone composition containing an organopolysiloxane with a cycloalkyl group; however, this cannot dispense with SiO2 units, wherefore a problem in its crack resistance.